Fibrous sheet material and method of producing the same

ABSTRACT

THE FIBROUS SHEET MATERIAL OBTAINED BY THE METHODCOMPRISING: (I) EXTRUDING A MOLTEN MIXTURE OF 30 TO 70 VOLUME PERCENT OF A CRYSTALLINE POLYMER (1) AND 70 TO 30 VOLUME PERCENT OF ANOTHER POLYMER (2), WICH IS INCOMPATIBLE WITH SAID CRYSTALLINE POLYMER (1) AND HAS A LOWER APPARENT MELT VISCOSITY THAN THE CRYSTALLINE POLYMER (1) UNDER THE EXTRUSION CONDITIONS TO MAKE A FILM CONSISTING OF SAID MIXTURE, IN WHICH THE CRYSTALLINE POLYMER (1) FORMS THE DISCONTINUOUS PHASE AND THE LATTER POLYMER (2) FORMS TE CONTINUOUS PHASE IN SAID FILM, AND HAVING THE CRYSTALLINE ORIENTATION IN THE LONGITUDINAL AXIS OF THE FILM; (II) LAMINATING MORE THAN TWO FILMS IN AN ORIENTATION SUCH THAT AT LEAST TWO OF SAID FILMS ARE IN DIRECTIONS AT AN ANGLE OF 60 TO 120* WITTH RESPECT TO EACH OTHER, AND THEN (III) BIAXIALLY STRETCHING SAID LAMINATE TO 2 TO 4 TIMES IN BOTH LENGTHWISE AND CROSSWISE DIRECTIONS SIMULTANEOUSLY TO PRODUCE A FIBROUS SHEET MATERIAL.

Oct. 31, 1972 H IDIENOBU" SOGI FIBROU$ SHEET MATERIAL AND METHOD OFPRODUCING THE SAME Filed DecQ lO 1970 g-o'ruzn I POLYMER LOG (swam RATE)Hiderzobu 50 BY ATTORNEY United States Patent 3,701,701 FIBROUS SHEETMATERIAL AND METHOD OF PRODUCING THE SAME Hidenobu Sogi, Kurashiki,Japan, assignor to Kuraray Co., Ltd., Kurashiki, Japan Filed Dec. 10,1970, Ser. No. 96,820 Claims priority, application Japan, Dec. 19, 1969,44/102,767, 44/102,768 Int. Cl. B32b 3/10 US. Cl. 156-229 16 ClaimsABSTRACT OF THE DISCLOSURE The fibrous sheet material obtained by themethod comprising:

(i) extruding a molten mixture of 30 to 70 volume percent of acrystalline polymer (1) and 70 to 30 volume percent of another polymer(2), which is incompatible with said crystalline polymer (1) and has alower apparent melt viscosity than the crystalline polymer 1) under theextrusion conditions to make a film consisting of said mixture, in whichthe crystalline polymer 1) forms the discontinuous phase and the latterpolymer (2) forms the continuous phase in said film, and having thecrystalline orientation in the longitudinal axis of the film;

(ii) laminating more than two films in an orientation such that at leasttwo of said films are in directions at an angle of 60 to 120 withrespect to each other, and then (iii) biaxially stretching said laminateto 2 to 4 times in both lengthwise and crosswise directionssimultaneously to produce a fibrous sheet material.

This invention relates to a fibrous sheet material produced from a filmconsisting of a mixture of a crystalline polymer and a polymer which isincompatible with the former, and particularly relates to a fibroussheet material produced from a film obtained by extrusion of a mixtureof the crystalline polymer and the other polymer, and furtherlaminating, and simultaneously biaxially stretching said film. Thefibrous sheet material as referred to herein is a sheet material formedby a group of fibers.

Conventional fibrous sheet materials comprise textiles and knit fabricsmade of filaments or fibers, and unwoven cloths prepared by: (1)needle-punching of a fibrous mat consisting of fibers cut to a suitablelength by random laying by the so-called dry method and (2) unwovencloths by the so-called wet method in which cut fibers are dispersed inwater or a similar liquid and formed into a sheet, a textile or a knitfabric, said cut fibers being formed by slitting a film and stretchingthe resultant fibers. Attempts also have been made to produce textilesand knit fabrics from a film prepared from a mixture of two types ofpolymers and is then slit and stretched into a fibrous condition.

The conventional fibrous sheet materials are, as described, formed froma fibrous material into a flat sheet material, whereas the presentinvention is intended to produce a fibrous sheet material directly froma film, and thereby essentially differs from conventional techniques.

A film obtained by extrusion of a mixture of two types of polymers whichare mutually incompatible is generally oriented in a lengthwisedirection, having high lengthwise strength, but very poor crosswisestrength, and such a film cannot be biaxially stretched. Therefore, thistype of film can hardly be used as a sheet material.

It is an object of this invention to overcome the differences ofconventional fibrous sheet materials by providing a fibrous sheetmaterial having both high lengthwise and "ice crosswise strength wherebysuch film can be biaxially stretched. Other objects will be apparentfrom the ensuing description of this invention in conjunction with thedrawing in which the figure is a graph showing the inter-relationship ofapparent viscosity and shear rate of the polymers used in preparing thefibrous sheet material of this invention.

According to this invention, the fibrous sheet material is obtained bylaminating a plurality of films, at least two of which are oriented atan angle of 60-120 with respect to each other, and furthersimultaneously and biaxially stretching the laminate, said films beingproduced by extrusion of a mixture of a crystalline polymer and anotherpolymer which are mutually incompatible. Only by the method oflaminating a film obtained by extrusion of a mixture of two types ofpolymers oriented in a certain direction with respect to each other, canthe film be biaxially stretched to give a product having high strength,both in the lengthwise and crosswise directions.

The fibrous sheet material of this invention comprises the followingfour types:

(1) one obtained by (a) laminating at least two films, at least two ofwhich are at a 60-120 angle with respect to each other, said films beingproduced by extrusion of a mixture of an incompatible crystallinepolymer and another polymer, and (b) by further simultaneously biaxiallystretching said laminate;

(2) one obtained by further heat-treating said sheet material (1);

(3) one obtained by extracting the polymer consisting of the continuouspart of the said sheet material (1) with a solvent for said polymer; and

(4) one obtained by heat-treating said sheet material (1) and furtherextracting the polymer comprising the continuous part of theheat-treated sheet material with a solvent for said polymer.

The crystalline polymers which can be used in this invention comprisepolymers having a high degree of crystallinity, used in melt formingsuch as polyethylene, polypropylene, polyamides and polyethyleneterephthalate, and the like.

The polymers used in this invention, in admixture with the crystallinepolymers comprise polymers which can be used in melt forming, such asethylene copolymers, polystyrene, styrene copolymers, ac'rylate resins,polyamides, cellulose acetate and the like. These polymers are requiredto be incompatible with crystalline polymers. It is important that therelationship between the melt viscosities of the crystalline polymer andthe polymer to be mixed therewith be proper, as shown in the figure.

The figure is a graph showing the relation between the apparentviscosity and the shear rate of a melt of a crystalline polymer formingthe discontinuous phase anda polymer forming the continuous phase in amixture of two types of polymers. Curve A shows the relation between theapparent viscosity and the shear rate of the crystalline polymer formingthe discontinuous phase, and curve B shows the relation between theapparent viscosity and the shear rate of the polymer forming thecontinuous phase. The value DL indicates the shear rate at the time theapparent viscosities of the crystalline polymer and the other polymerare equal. In the production by extrusion of the film from the mixtureof the two types of polymers, with reference to the conditions oftemperature and shear rate of the extrusion, it is essential that theapparent viscosity of the crystalline polymer is higher than that of theother polymer mixed therewith. The apparent viscosity and the shear rateof each polymer as referred to herein are determined by applying adifference of pressure P to both ends of a capillary tube with a radius(R) of 0.05 cm. and a length (L) of 1 cm., and

measuring the flow rate Q of the polymer, and then solving the followingformula:

1rP R4 Apparent viscosity m (i) 2 Shear rate 7r R3 The relation betweenthe apparent viscosity and the shear rate given by the above method isshown in the figure wherein, curve A shows the crystalline polymer,while curve B shows the otherpolymer. That the apparent viscosity of thecrystalline polymer is higher than that of the polymer mixed therewithunder conditions of extrusion means that the molding proceeds in amanner such that the shear rate at the molding temperature becomes lowerthan DL. By satisfying this condition, the crystalline polymer forms the.discontinuous phase in the mixture, and the polymer mixed therewithforms the continuous phase and accordingly the crystalline polymer turnsinto a fibrous form, the lamination proceeds easily as will be explainedhereinafter, and effective extraction is carried out thereby giving anextracted substance which will have gas-permeability. When thedifference in melt viscosity between the crystalline polymer and thepolymer mixed therewith is too great, it is extremely difficult to mixboth homogeneously. It is, therefore, desirable that the apparentviscosity of the crystalline polymer under the extrusion conditionsatisfy the following formula:

When the above conditions are satisfied, mixing can be carried outrelatively homogeneously.

The proportion of polymers in the mixture is desirably about 30-70 vol.percent of crystalline polymer (forming the discontinuous phase in themixture) and 70-30 vol. percent of the other polymer. If the crystallinepolymer content is less than about 30 vol. percent, fibrous flatmaterial .having a high strength cannot be produced while if it is morethan about 70 vol. percent, the crystalline polymer occasionally failsto form a discontinuous phase and the extraction of the other mixedpolymer cannot be efliciently effected as will be explained later.

-For homogeneous mixing of the crystalline polymer and the otherpolymer, it is necessary to select the best method of mixing, based uponthe polymers which are used, the mixing proportion, the melt iscositiesof both polymers and so on. For homogeneous mixing various methods canbe used, such as mixing the polymers in pellet or powder. form, mixingthe polymers on rolls, mixing the polymers in a B-anbury mixer, mixingthe polymers in molten condition in an extruder, etc. In the case of acombination of polymers, the homogeneous mixing of which is extremelydiflicult, the polymers can be easily and homogeneously mixed at aslow atemperature as possible, but above the melting point of the crystallinepolymer.

Extrusion conditions for producing the film by extruding the mixture ofthe two types of polymers mixed by the above-mentioned methods should bedetermined by the combination of the two types of polymers to be used,but it is generally possible to extrusion mold by selecting extrusionconditions which are close to those for the extrusion of the crystallinepolymer. However, it is necessary that the temperature conditions at theback of the cylinder of the extruding machine is suitable for the typeof polymer which forms the continuous phase. I

In the present invention, it is also important to properly laminate theoriented film of the mixture of the crystalline polymer and the otherpolymer. The temperature for lamination should be higher than initialflow temperature of the polymer forming the continuous phase,

but lower than the melting point of the crystalline polymer forming thediscontinuous phase. When laminating several sheets of film, it isnecessary that at least two sheets of film are oriented at an angle of60-120 to each other. At any other angles, the film will be split in thebiaxial stretching, or the directionality of the product obtained by thebiaxial stretching will be increased, resulting in an extremely lowstrength in one direction. Lamination in the direction of orientationhaving angles as referred to above, includes the case wherein a. rotarydie is used and the direction of orientation continuously changes. Thefilm laminated in continuously changing directions of orientation hasthe same effect as several sheets of film laminated in differentorientation direc/ tions, hence it is included in this invention.

It is important to biaxially stretch the laminate of the film of themixture of the two types of polymers to increase the strength thereof.Simultaneous biaxial stretching is preferrable. Non-simultaneous biaxialstretching is not desirable as it causes breaking of the film. Theelongation temperature is determined according to the combination of thecrystalline polymer and the other polymer. For example, whenpolypropylene is used as the crystalline polymer, desirable temperatureis about -150 C., when polyamides are used, a desirable temperature 1sabout 60-180 C., and when polyethylene terephthalate is used, adesirable temperature is about 80-180 C. By suitably combining thecrystalline polymer and the otherpolymer and selecting suitableelongation temperatures, it is possible to apply cracks uniformly to theelongated film. The multiple of elongation by biaxial stretching 1sdesirably about 2-4 times in both the lengthwise and crosswisedirections, but maximum useful elongation depends on the combination ofthe two types of polymers, the proportion of the polymers and the mixmgconditlons.

Heat-treatment optionally employed in the product1on of the fibroussheet material of this invention, can serve to decrease cracks formed byelongation, and improve dimensional stability thereof. When the polymerforming the continuous phase is extracted, film which is not heattreatedwill strip off at the laminated interface, but heattreated film willnever strip olf, and the surface after the extraction is extremelysmooth. While the heat-treating conditions depend on the combination ofthe two types of polymers, the heat-treatment temperature is desirablyhigher than the elongation temperature and lower than the melting pointof the crystalline polymer used. The heat-treatment temperature whenpolypropylene is used as the crystalline polymer is desirably about -1600., about -190 C. for polyamides and about 160-200 C. for polyesters.The film obtained after heat-treatment generally has higher ductility.

Extraction as is optionally used in the production of the fibrous sheetmaterial of this invention refers to extraction of the polymer formingthe continuous phase of the film of the mixture. The solvent used insaid extraction should dissolve the other polymer, but should notdissolve the crystalline polymer forming the discontinuous phase. It isdesirable to extract 50-99 vol. percent of the other polymer. Ifextraction is of less than about 50 vol. percent, the hand remainsessentially the same as fiber which has not been extracted, and if morethan 99 vol. percent is extracted, stripping at the laminated interfacemay occur or the form of the remaining fiber may collapse. Onthe surfaceof film which has been extracted as above, the pattern of fibrousmaterial will appear, giving it an appearance similar to Japanese washipaper.

The fibrous sheet material of this invention is preferably obtained byextrusion molding a mixture of polypropylene and the saponified productof ethylene/ vinyl acetate copolymer, and laminating sheets of theresultant fihn in an orientation angle of 60-120, and furthersimultaneously and biaxially stretching the laminate. Only by laminatingthe film prepared from a mixture obtained by extrusion molding in saidorientation direction, can the film be biaxially stretched, withimproved lengthwise and crosswise strength, and will the strength of theoriented polypropylene be fully utilized by the elongation.

The preferred fibrous sheet material of this invention comprises fourtypes: v (1) One obtained by laminating the film prepared by extrusionmolding of a mixture of polypropylene and the saponified product ofethylene/vinyl acetate copolymer which are mutually incompatible,oriented at a certam angle with respect to each other, and furthersimultaneously and biaxially stretching said laminate;

(2) One obtained by heat-treating stretched film (l); (3) The stretchedfilm (1) from which the saponified product of ethylene/vinyl acetatecopolymer is extracted with a solvent therefore; and

(4) The heat-treated film (2) from which the saponified product ofethylene/vinyl acetate copolymer forming the continuous phase isextracted with the solvent therefor.

The stretched film (1) has a hand resembling that of Japanese washipaper; the heat-treated film (2) has a hand like that of parafiin paper;and the extracted films (3) and (4) have a hand like that of paper orunwoven cloth. These fibrous sheet materials can be obtained when thefollowing requirements are satisfied.

The polypropylene used in this invention is an isotact1c polypropyleneor a copolymer in which ethylene and/ or a like monomer which iscopolymerizable with propylene, is copolymerized therewith. The degreeof polymerization of polypropylene should be determined in respect tothe saponified product of the ethylene/vinyl acetate copolymer, by ASTMD-123 8-52T, and should be in the range of 0.2-10 g./ 10 min. of meltindex measured at temperature 230 C., and a load of 2160 g.

The saponified product of ethylene/vinylacetate copolymer used in thisinvention is an ethylene/vinylacetate copolymer whose vinyl acetategroups are replaced by vinyl alcohol groups, said copolymer consistingof 30-45 mol percent ethylene and 70-55 mol percent vinylacetate, andthe percentage y of conversion of vinylacetate groups into vinyl alcoholgroups should satisfy the following formula wherein x is the molepercent ethylene content of the ethylene/vinylacetate copolymer:

When a saponified product of the ethylene/vinylacetate copolymer whichsatisfies the above formula is used, the resultant fi-lmdoes not stickto the clips of the biaxial stretching apparatus and does not break inthe biaxial stretching step, i.e., the cracks are evenly distributed insaid film. When said saponified product of ethylene/vinylacetatecopolymer and polypropylene is used, the relation between the meltviscosities of the polymers at the time of extrusion molding of the filmof the mixture is important. When preparing a film of the mixture ofpolypropylene and the saponified product of ethylene/vinylacetatecopolymer by extrusion molding under the conditions of extrusiontemperature and the shear rate, it is essential that the apparentviscosity of polypropylene is higher than that of the saponified productof ethylene vinylacetate copolymer. The apparent viscosities and theshear rates of both polymers are determined by measuring the flow rate Qof the polymer, applying a difference of pressure P to both ends of acapillary tube having a radius R of 0.05 cm. and a length L of 1 cm.,and solving Formulae i and ii described above.

The relation between the apparent viscosity and the shear rate describedabove is shown in the figure. Curves A and B show this relation forpolypropylene and the saponified product of ethylene/vinylacetatecopolymer. That the apparent viscosity of polypropylene is higher thanthat of the saponified product of ethylene/vinylacetate copolymer underextrusion molding conditions, signifies that extrusion molding iscarried out under conditions such that the shear rate at the moldingtemperature is smaller than DL. When the above conditions are satisfied,

polypropylene is caused to form the discontinuous phase in the mixtureand the saponified product of ethylene/ vinylacetate copolymer forms thecontinuous phase. As a result, polypropylene takes the form of fibersand can be easily laminated as will be explained hereinafter, and theextrusion efficiency of the saponified product of ethylene/vinylacetatecopolymer is increased, and further the extracted product will havegas-permeability. When the difference in the viscosities ofpolypropylene and the saponified product of ethylene/vinylacetatecopolymer is great, it is extremely difficult to mix the twohomogeneously, but when the apparent viscosity of polypropylenesatisfies the following formula under the extrusion molding conditions,the two can be mixed homogeneously relatively easily.

Apparent viscosity of polypropylene Apparent viscosity of saponifiedproduct of ethylene] vinylacetate copolymer 30-70 vol. percentpolypropylene to 70-30 vol. percent saponified product ofethylene/vinylacetate copolymer is a desirable mixing proportion forthese two polymers. When the polypropylene content is less than 30 vol.percent a strong fibrous fiat material cannot be obtained, while whenmore than 70 vol. percent is used, polypropylene may occasionally failto form a discontinuous phase in the mixture, and furthermore theefiiciency in extraction of the saponified product ofethylene/vinylacetate copolymer will be reduced.

For homogeneous mixing of polypropylene and the saponified product ofethylene/vinylacetate copolymer, the polymers, the mixing proportion,the melt viscosity, etc. should be considered in choosing the specificmixing technique. Useful mixing methods comprise mixing the polymers inpellet form or powder form or mixing the polymers in molten condition onmixing rolls, Banbury mixers, extruding machines, etc. In the case of acombination of polymers which cannot be easily mixed homogeneously,homogeneity will be improved by mixing the polymers at as low atemperature as possible, but higher than the melting point ofpolypropylene.

When the film made by extrusion molding of the mixture of polypropyleneand the saponified product of ethylene/vinylacetate copolymer by theabove method is used, the processing conditions should be determinedaccording to the combination of the two polymers, and it is possible toextrusion mold the mixture by selecting conditions akin to the extrusionmolding conditions for polyropylene, and the temperature at the back ofthe cylinder of the extruding machine should be determined according tothe type of the saponified product of ethylene/vinylacetate copolymer.

As noted above, it is also important to correctly laminate the film ofthe mixture of polypropylene and the saponified product ofethylene/vinylacetate copolymer. The laminating temperature is requiredto be higher than the initial flow temperature of the saponified productof ethylene/vinylacetate copolymer, but lower than the melting point ofpolypropylene. In laminating, a plurality of sheets of film, at leasttwo sheets should be oriented in directions at an angle of 60-120 withrespect to each other. Only by satisfying the abovementioned conditionswill biaxial stretching which constitutes one of the most importantfactors of the invention become possible. When these conditions are notsatisfied, the film may break during biaxial stretching, and the productobtained by the biaxial stretching will have directionality, i.e., adirection in which it is extremely weak. The lamination in certainorientation also includes the case wherein the orientation directioncontinuously changes as when, for example, a rotary die is used. Whilesaid film is not laminated, when its surface is cut at a right angle tothe direction of thickness, the two sheets of film have differentorientation directions with respect to each other, and thus such a filmexhibits the same effects as the laminate of several sheets of the film7 having difierent orientation directions, and is included in thisinvention.

The biaxial stretching of the laminated film of the mixture ofpolypropylene and the saponified product of ethylrate of extractionshould be 50-99 vol. percent of the saponified product ofethylene/vinylacetate copolymer. If the rate of extraction is less than50 vol. percent, the hand of the film remains the same as afterbiaxially ene/vinylacetate copolymer as abovementioned is imstretched,and if it is more than 99 vol. percent, stripping portant for increasingthe strength of the film. P'articuat the laminated interface may occuror the form of the larly, simultaneous biaxial stretching is desirable,and nonextracted product may collapse. The product thus exsimultaneousbiaxial stretching is not desirable, as the film tracted will show afibrous pattern on its surface, such as then may be split. An elongationtemperature of l20-15 0 that of paper or unwoven cloth. C. is desirable.By selecting suitable elongation tempera- The following examples aregiven to further illustrate, tures, cracks will be distributed evenly inthe elongated without limiting this invention. film. Simultaneousbiaxial stretching giving an elongation of 2-4 times in both lengthwiseand crosswise directions EXAMPLES is desirable, but the multiple ofmaximum possible elonga- Polypropylene (crystalline polymer) and theother tion depends on the combination of the polymers, mixing polymer inthe form of pellets were mixed in a proporproportion and mixingconditions. tion of 50:50 vol. percent, and extruded at 235 C. and Inproduction of the fibrous flat material of this invenat shear rate of200 sec.- into a film having a thickness tion from a mixtue ofpolypropylene and the saponified of 0.2 mm. Two sheets of the film werelaminated at a product of ethylene/vinylacetate copolymer,heat-treattemperature 10-l5 C. higher than the initial fiow temment isoptionally applied to reduce the number of size perature of the polymerforming the continuous phase, of the cracks produced by the elongationand the cracks and were further subjected to simultaneous biaxialstretchwill be distributed evenly and the dimensional stability ing at130 C., and then heat-treated at 150 C. The perwill be improved. Whenthe saponified product of ethylformances of the film thus obtained andof the film from ene/vinylacetate copolymer forming the continuous phasewhich the polymer forming the continuous phase was exin the film of themixture, is extracted with a solvent theretracted with a solventtherefor, are shown in Table 1.

TABLE 1 (1) Crystalline Apparent vi)scosity Extracted productUnextracted product lymer (pols Rate of g iscontinuous (2) Other polymerMultiple Heat- Elongaextraction Elonga- Ex. phase in the mixed(continuous Polymer Polymer of elongatreat- Strength tion 01. Strengthtion No. film) phase in the film) (l) (2) tion ment (kg/cm!) (percent)percent) (kg/cm!) (percent) 1 Polypr0py1ene Ethylene-vinylace- 6.50X103. x10 3X3 N0-. 177 49 =96 92 27 tate copolymer. I 2 d0 do 6. Xl0 3.235x10 3X3 Yes--- 180 o Polystyrene- 6.50X10 2. 47x10 3X3 No 382 d0. d050X10 2. 47X10 3X3 Yes--- 395 ..d0 do 50X10 2. 47X10 2.5X2.5 N0 334 dodo 6 50X10 2. 17x10 25x25 Yes 350 do do 6 50X10 2. 47X1 2X2 N0 182 d0 d06. 50X10 2. 47x10 2X2 Yes-.. 189 do Styrene/acrylonltrile 6.50 105.70X10 3X3 No 322 copolymer. b 10 -d0 do 6. 50 10 5. 70X10 3X3 Yes-.-330 11 d0 Methyl methacrylate-. 6. 50Xl0 5.50X10 3X3 No 554 12 do do 6.50Xl0 5. 50Xl0 3X3 Yes--. 565

I Content of ethylene: 86 mol percent.

b Content of styrene: 70 weight percent. a Solvent: toluene.

d Solvent: toluene.

' Solvent: ethylacetate.

fore, the laminate which was not heat-treated may strip off at thelaminated interface while one which has been heat-treated will neverstrip off, and the surface of the film after the extraction is extremelysmooth. By heat-treatment, the strength of the film is somewhatincreased, and the ductility is markedly improved.

The extraction which is optionally employed in the production of thefibrous sheet material of this invention means the extraction of thesaponified product of ethylene/vinylacetate copolymer forming thecontinuous phase in the film with a solvent therefor. As solvents forthe saponified product of ethylene/vinylacetate copolymer, a mixture ofmethanol and water, dimethylformamide, dimethylsulfoxide,epichlorohydrin, etc. can be used. The

EXAMPLES 13-28 Nylon 6 (polycaprolactam) as the crystalline polymer andthe other polymer used in Examples 1 to 12 were mixed in a proportion of50:50 vol. percent and extrusion molded at 235 C. and at a shear rate of200 sec.- into a film having the thickness of 0.2 mm. Films were thenlaminated in an orientation at right angles with respect to each otherat a temperature 10-15" C. higher than the initial flow temperature ofthe polymer forming the continuous phase, and further simultaneously andbiaxially stretched at 120 C. Then the laminate was heat-treated at 180C. The performances of the resultant film and the film from which thepolymer forming the continuous phase was extracted, are shown in Table2.

TABLE 2 Extracted product (1) Crystalline Apparent v1scos1ty Unextractedproduct p ymer (P0156) Rate of (discontinuous (2) Other polymer MultipleHeat- Elongaextraction Elonga- Ex. phase in the mixed (cont1nuousPolymer Polymer of elongatreat- Strength on 01. Strength tion No. film)phase in the film) (1) (2) tion ment (kgJcm) (percent) percent)(kg/c111, (percent) 13".-- Nylon 6 Ethylene-vinyl ace- 1.80X10 3.35x10 32X2 No- 402 87 268 167 tate copolymer. do 1.80Xl0 3.35X10 5 2X2 Yes-.-405 75 270 180 Polystyren 1.80X10 4 2. 1.7)(10 2X2 N0 385 79 91 202 41d0 1.80X10 2.47X1Ct 2X2 Yes 390 86 91 205 70 Styrene/acrilonitrile1.80X10 6.70X10 2X2 No 235 89 131 56 copolymer. 18 do do 1.80Xl0 5.70X103 2X2 Yes--- 237 89 132 75 19 do Methylmethacrylateu 1.80Xl0 5.5OXl0 2X2NO 482 122 90 268 149 20 .-d0 "do 1.80X10 5.50X10 2X2 Yes..- 485 143 90270 9 EXAMPLES 21-24 Polyethylene terephthalate as the crystallinepolymer and the other polymer used in Examples 1-12, in pellet form weremixed in a proportion of 50:50 vol. percent, and extrusion molded at 270C. at the shear rate of 200 sec.- into a film 0.2 mm. thick and twosheets of the film were laminated at a temperature -15 C. higher thanthe initial flow temperature of the polymer forming the continuous phasein orientation directions whereby they intersected at right angles, thensimultaneously and biaxially stretched at 130 C., and further heattreated at 190 C. The performances of the resultant films and the filmsfrom which the polymer forming, the continuous phase were extracted withthe solvent therefor, are shown in Table 3.

EXAMPLES 25-28 Polypropylene and ethylene vinylacetate copolymer used inExamples 1 and 2, but having diiferent propor- EXAMPLES 29-52 50 vol.percent of polypropylene (melt index: 0.4) and 50 vol. percent of thesaponified product of ethylene/ vinylacetate copolymer containing 32.9mol percent ethylene (72.8 percent saponification), both in pellet form,were mixed and made into pellets of the mixture, using a rapidcompression type screw at 220 C. From the pellets was produced a 0.2 mm.thick film at a temperature of 220 C. and a shear rate of 200 sect- Theapparent viscosity of polypropylene under said extrusion conditions was7.40 10 poise and that of the saponified product ofethylene/vinylacetate copolymer was 700x10 poise. Several sheets of theresultant film of the mixture were heat-laminated at 155-160 C. in rightangle orientation and simultaneously biaxially stretched. Theheat-treatment was completed in a minute at 150 C. In the extraction, amixture of 80 wt. percent methanol and wt. percent water was used at 50C. The performances of tions were mixed and processed by the method ofExam- 20 the respective products are shown in Table 5.

TABLE 5 Number 01 Elonga- Heat- Thlek- Modulus oi Elongasheets tlontreat- Extraction ness Weight elasticity Strength on Treatment laminatedmultiple ment (percent) (mm.) (g./m. (kgJcmfi) (kg/cm!) (percent) 4 0.185 88. 9 1, 060 120 16. 0 3 8-33 13-3 E3 132 32'; 4 0: 120 52: 5 1: 20014s 14: s 6 0. 140 71. 8 1, 300 199 22. 0 8 0. 166 97. 8 1, 540 207 22.2 4 0. 113 74. 2 1, 190 109 44. 4 6 0. 152 122. 7 1, 440 139 71. 4Heat-treated and elongated 2 82 33 gig :33 gg 22:3 6 0. 118 75. 6 1, 570159 37. 1 8 0. 155 100. 4 1, 750 222 54. 1 4 95. 1 0. 157 46. 3 737 50.5 7. 1 6 96. 4 0. 180 61.8 997 70. 2 7. 1 Elongated, and extracted i 3%:31% i3): 6 90. 5 0. 113 36. 0 1, 320 115 9. 2 8 98. 4 0. 134 43. 4 1,320 109 8. 7 4 98. 6 0. 108 39. 7 848 61. 8 13. 4 6 99. 0 0. 151 61. 9767 56. 0 10. 5 Elongated, Heat-treated and ex- 2 33:3 3: 3% 3;}; $5;igjg mmede 91. 7 0. 092 :17. 5 1, 320 130 17. 4. 8 89. 9 0.133 57. 4 1,180 129 18. 0

ples l-12, and the performances of the resultant products are shown inTable 4.

Also, polyethylene terephthalate and polystyrene used in Examples 23-24,but having dilferent proportions were mixed and processed by the methodof Examples 1-12 and the performances of the resultant products areshown in Table 4.

EXAMPLES 53-5 6' 40 vol. percent of polypropylene and 60 vol. percent ofthe saponified product of ethylene/vinylacetate copolymer, in pelletform as used in Example 1 were mixed and the pellets of the mixture wereprepared under the same conditions as of Example 1 from which was pro-TABLE 3 Extracted product (1) Crystalline Apparent viscosity Unextractedproduct polymer (poise) Rate of (discontinuous (2) Other polymerMultiple Heat- Elongaextraction Elonga- Ex. phase in the mixed(continuous Polymer Polymer 01 elongatreat- Strength tlon (vol. Strengthtion N o. film) phase in the film) (1) (2) tion ment (kgJcmJ) (percent)percent) (kgJcmJ) (percent) 21--- Polyethylene Ethylene/ethyl acry- 1.04x10 1.60X10' 2X2 No- 637 16 b 87 367 71 terephthalate. late copolymer.22 do do 1. 04X10 1. 60X10' 2X2 Yes- 637 53 87 371 80 23 (inPolystyrene 1. 04x10 1. 60X10' 2. 5X2.5 N0.--- 548 73 Q 77 356 108 24 dodo 1. 04x10 1.60X10' 2. 5X2.5 Yes--- 546 80 77 355 112 a Content ofethylene: 92 mol percent. 5 Solvent: benzene. Solvent: toluene.

TABLE 4 Extracted product (1) Crystalline Apparent viscosity Unextractedproduct polymer (poise) Rate of (discontinuous (2) Other polymerMultiple Heat- Elongaextraction Elonga- Ex. phase in the mixed(continuous Polymer Polymer 0t elongatreat- Strength t1on (v01. Strengthtion No. film) phase in the film) (1) (2) tron ment (kg/cm!) (percent)percent) (kg/cm!) (percent) 25 Polypropylene.. Ethylene-vinylaced 60 d40 3X3 Yes-.. 255 b 94 163 80 tate copolymer. 9n dn dn 6 I d 60 3X3Yes-.- 102 80 98 80 33 27. Polyethylene Polystyrene d 60 d 40 2.5)(2. 5Yes... 730 v 70 435 128 tetephthalate. 28 do do 11 40 I! 2.5X2.5 Yes-..363 83 303 58 e Content of ethylene: 86 mol percent. b Solvent: toulene.e Solvent: toulene. Volume percent.

duced the laminated and biaxially stretched films showing theperofrmances as given in Table 6.

EXAMPLES 57-64 50 vol. percent of polypropylene (melt index: 0.4) andmer (1) forms the discontinuous phase and the latter polymer (2) formsthe continuous phase in said film, and having its orientation in thelengthwise direction Of the film;

(ii) laminating a plurality of sheets of said films in such 50 176mmt ofthe Salwmfifid P t (80.9% saponan orientation that at least two sheetsof said films ification) of ethyle'ne/vinylacetate copolymer contalnarei t d t n angle of 60 to 120 with respect ing 39.4 mol percent ethylene,both in pellet form were t h h d th mixed and pellets of the mixturewere produced by a rapid (iii) biaxially stretching said laminate 2 to 4times in transition metering-type screw at 220 The pellets lengthwiseand crosswise directions simultaneously Were then formed into a thlck,at a at a predetermined temperature to produce a fibrous perature of 220C. and a shear rate of 200 sec- The sheet material consisting of saidmixture and having apparent viscosity of polypropylene was 7.40 10 poiseboth a discontinuous and continuous phase. and that of the saponifiedproduct of ethylenelvinylacetate 2. The method'of producing a fibroussheet material in copolymer was 40 10 poise under the extrusionconaccordance with claim 1 which comprises the further step ditions. Sixsheets of the film of the mixture were heatf; laminated at ISO-155 C. in511611 orientation that the diextracting 50 to 9-9 volume percent ofpolymer (2), rections of the films intersected at right angles withrespect ith a l t f polymer (2) hi h l t d to each other, thensimultaneously and biaxrally stretched not dissolve polymer ('1). at 130C., heat-treated at 150 C. for one minute, and 3. The method ofproducing a fibrous sheet material in further extracted using a mixtureof '80 wt. percent methaccordance with claim 1 which comprises thefurther step anol and 2 0 wt. percent water at C. The properties of: ofthe respective products are shown in Table 7. heat-treating the fibroussheet material produced by the TABLE 0 Thick- Modulus of Example NumberElongation Heatness Weight elasticity Strength Elongation No. ol sheetsmultiple treatment (mm.) (gJmJ) (kgJcmfl) (kgJcmJ) (percent) 4 0.18983.8 043 41.9 41." 6 0. 255 140.1 967 70.1 70. 4 0. 126 so. 6 836 21s. 325. a s o. 102 80.8 1, 032 40. 1 40. 4

TABLE 7 Elonga- Heat- Thick- Modulus of Ex. tion treat- Extraction nessWeight elasticity Strength Elongation No. Treatment multiple m t(percent) (mm.) (g./m. (kgJcmJ) (kg/cm!) (percent) 3x3 No 0. 233 147.11,680 148 16.0 31s.--. Emgmd- 3% 3. 138 5 22 w 13% 102 811:Elongatedmdhe" treated esIIIIIIII 0:522 mfg 1:783 15 2 2 0..-- $11:El'mgated and timed 4x; 87.2 8.1%: i128 iig %.2 gi j z extracted i524r5313: 3%? 83533 5332 {$53 3333 13;;

EXAMPLES -72 method of claim 1 at a temperature which is higher 50 vol.percent of polypropylene (melt I and 45 than the stretching temperatureof step (iii). 50 VOL Percent of thfi saponified Prodlmt (84.6% sapon-4. The method of producing a fibrous sheet material in ification) ofethylene/vinylacetate copolymer contalnlng accordance with claim 1 whichcomprises the further steps 39.4 mol percent ethylene, in pellet formwere mixed and f; made i -0 a fi laminated, Stretched, ed aheat-treating the fibrous sheet material produced by the extracted underthe conditions described in Examples 29- 50 method of claim 1 at atemperature which is higher 36, and the performances of the respectiveproducts are than the stretching temperature of step (iii), and thengiven in Table 8. Under the extrusion conditions, the apextracting 50 to99 volume percent of polymer (2) with parent viscosity of polypropylenewas 7.40 10 p o1se a solvent for polymer (2) which does not dissolvewhile that of the saponified product of ethylene/vmylpolymer (1).acetate copolymer was 290x10 poise.

TABLE 3 Elonga- Heat Thick- Modulus of EX. tlon treat- Extraction nessWeight elasticity Strength Elongation No. Treatment multiple ment(percent) (mm. (gJmJ) (kg/em!) (kg/cm!) (percent) a 3 N 0.263 155.71,200 133 18.8 ggIIIII Elmgmd 3;; $8 0.167 13.2 1,310 146 13.2 25333::Elongatedwd hemmed & v illiililiii 1 62:3 h g ll; 7 31:: Ekmgated andmeted 4&4 N31: 9515 01141 40.1 553 3010 s10 E1o m a: as; a: as; as a: a;:1;

What is claimed:

1. A method of producing a fibrous sheet material which comprises:

(i) extruding a molten mixture of 30 to volume percent of a crystallinepolymer (1) and 70 to 30 volume percent of another polymer (2), which isincompatible with said crystalline polymer and has a lower apparent meltviscosity than the crystalline polymer under extrusion conditions, tomake a film consisting of said mixture, in which the former poly- S. Amethod of producing a fibrous sheet material which comprises:

(i) extruding a molten mixture of 30 to 70 volume percent ofpolypropylene and 70 to 30 volume percent of the saponified product ofethylene/vinylacetate copolymer containing 30 to 45 mol percent ofethylene which is incompatible with said polypropylene and has a lowerapparent melt viscosity than that of polypropylene under the extrudingconditions, said copolymer satisfying the following formula wherein y isthe percent of saponification and x is the mole percent of ethylene:

to make a film consisting of said mixture, in which polypropylene formsthe discontinuous phase and said copolymer forms the continuous phase insaid film, and having its orientation in the lengthwise direction of thefilm;

(ii) laminating a plurality of sheets of said films in such anorientation that at least two sheets of said film are oriented at anangle of 60 to 120 with respect to each other; and then (iii) biaxiallystretching said laminate 2 to 4 times in lengthwise and crosswisedirections simultaneously at a temperature of from 120 to 150 C. toproduce a fibrous sheet material consisting of said mixture and havingboth a discontinuous phase and a continuous phase.

6. The method of producing a fibrous sheet material in accordance withclaim 5 which comprises the further step of:

heat-treating the fibrous sheet material produced by the method of claim5 at a temperature of from 130 to 160 C.

7. The method of producing a fibrous sheet material in accordance withclaim 5 which comprises the further step of:

extracting 50 to 99 volume percent of the saponified product of ethylenevinylacetate copolymer with a solvent for said copolymer which is not asolvent for polypropylene under conditions of extraction.

8. The method of producing a fibrous sheet material in accordance withclaim 5 which comprises the further steps of:

heat-treating the fibrous sheet material produced by the method of claim5 at a temperature of from 130 to 160 C.; and then extracting 50 to 99volume percent of said copolymer with a solvent for said copolymer whichis not a solvent for polypropylene under conditions of extraction.

9. A fibrous sheet material produced by the process which comprises:

(i) extruding a molten mixture of 30 to 70 volume percent of acrystalline polymer (1) and 70 to 30 volume percent of another polymer(2), which is incompatible With said crystalline polymer and has a lowerapparent melt viscosity than the crystalline polymer under extrusionconditions, to make a film consisting of said mixture, in which theformer polymer (1) forms the discontinuous phase and the latter polymer(2) forms the continuous phase in said film, and having its orientationin the lengthwise direction of the film;

(ii) laminating a plurality of sheets of said films in such anorientation that at least two sheets of said films are oriented at anangle of to with respect to each other; and then (iii) biaxiallystretching said laminate 2 to 4 times in lengthwise and crosswisedirections simultaneously at a predetermined temperature to produce afibrous sheet material consisting of said mixture and having both adiscontinuous and continuous phase.

10. The fibrous sheet material of claim 9 wherein said crystallinepolymer is a member selected from the group consisting of polyethylene,polypropylene, polyamides and polyethylene terephthalate.

11. The fibrous sheet material of claim 9 wherein said polymer (2) is amember selected from the group consisting of ethylene copolymers,polystyrene, styrene copolymers, acrylates, polyamides and celluloseacetate.

12. The fibrous sheet material of claim 9 wherein the crystallinepolymer is a polypropylene.

13. The fibrous sheet material of claim 9 wherein the polymer (2) is thesaponified product of ethylene/vinylacetate copolymer containing 30 to45 percent of ethylene.

14. The fibrous sheet material produced by extracting 50 to 99 volumepercent of polymer (2) from the biaxially stretched laminate of claim 9with a solvent for polymer (2) which solvent does not dissolve polymer(1).

15. The fibrous sheet material produced by subjecting the fibrous sheetmaterial of claim 9 to the further step of heat-treating said fibroussheet material at a temperature which is higher than the stretchingtemperature of step (iii) of claim 9.

16. The fibrous sheet material produced by subjecting the fibrous sheetmaterial of claim 9 to the further steps of heat-treating said fibroussheet material at a temperature which is higher than the stretchingtemperature of step (iii); and then extracting 50 to 99 volume percentof polymer (2) with a solvent for polymer (2) which does not dissolvepolymer (1).

References Cited UNITED STATES PATENTS 3,531,439 9/1970 Fukushima et al.156305 X 3,131,113 4/1964 Arbit ct al 156--244 X 3,255,065 6/1966Wyckoif 156229 3,384,531 5/1968 Parrish 156229 X 3,539,439 11/1970Calderwood et a1. 156229 X 3,567,539 3/1971 Schirmer 156229' X 3,092,8916/1963 Baratti 2882 RALPH S. KENDALL, Primary Examiner C. WESTON,Assistant Examiner U.S. Cl. X.R.

UNITED STATES PATENT OFFICE I I CERTIFICATE OF CORRECTION JET/noisier:NO. 3,701,701 Dated October 31, 1972 Inventor (s) Hidenobu Sogi It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

mus)

Column 5, line 52, insert "two" after "the"'and before "polymers" Column12, Table 8, in Ex. No. 72 under Elongation (percenty "5. 7" should be15.7 r

Signed and sealed this 1st day of January 197L|..

(SEAL) Attest:

EDWARD M.FLETCHER,JR. RENE D. TEGTME YER I Attesting Officer Acting.Commissioner of Patents

